Silica-resin direct filling material and method of preparation



United States Patent s 194 784 SILICA-RESIN DIRECT FILLING MATERIAL ANDMETHOD OF PREPARATION Rafael L. Bowen, Washington, D.C., assignor to theUnited States of America as represented by the Secretary of Commerce NoDrawing. Original application Jan. 30, 1959, Ser.

No. 790,308, now Patent No. 3,066,112, dated Nov. 27,

1962. Divided and this application May 1, 1962, Ser- 4 Claims. (Cl.26041) The present invention is a division of my application Serial No.790,308, filed January 30, 1959, now US. Patent 3,066,112, issuedNovember 27, 1962.

This invention relates to an insoluble, esthetic direct filling materialfor anterior teeth suitable for use in dental practice and the like andto methods for preparing the same.

The two direct filling materials available to dentists at the presenttime capable of matching the teeth in appearance are the silicatecements and the methyl methacrylate-based resins. Silicate cements notonly lack strength at the edges thereby presenting difiiculties inconnection with building up cutting edges and corners but they are alsosoluble in mouth fluids. The methyl methacrylate direct filling resinsnow in use, on the other hand, have a relatively high shrinkage uponhardening, high coefficient of thermal expansion, low stiffness and lowcompressive strength.

It is therefore an immediate object of the present invention to providean improved direct filling material that is less soluble than silicatecements and more dimensionally stable than methyl methacrylate directfilling resins and which is suitable for restoring anterior teeth.

Another object of the invention is to provide an improved fillingmaterial and process for preparation thereof whichis suitable for dentalwork wherein said filling.

material is quick-setting and of improvedstrength and durability.

It is an additional object of the present invention to provide a fillingmaterial having a low shrinkage upon hardening, low coefficient ofthermal expansion, high stiffness and high compressible strength.

Other, further, and more specific objects of this invention will becomereadily apparent to persons skilled in the art from a consideration ofthe following description, including specific examples.

The dental material of the present invention consists of approximately70 percent by weight of finely divided fused silica particles that canbe used as untreated aggregate or which may optionally be treated with afinishing or keying agent and which particles are bound together byabout 30 percent by weight of a crosslinked organic polymer of originalcomposition and chemical structure.

In accordance with one embodiment of the present invention the reactionproduct of bisphenol A and glycidyl methacrylate, thinned withtetraethyleneglycol dimethacrylate and activated withdimethyl-para-t-oluidene hardens at room temperature in about 3 minuteswhen mixed with fused silica powder containing benzoyl peroxide. Thistooth-colored solid had a compressive strength of 11,000 pounds persquare inch in accordance with the.

American Dental Association Specification No. 9. When the filler isoptionally treatedas by the addition of a keying agent such as vinylsilane, the compressive strength was increased to 16,000 p.s.i. Theoptical opacity of such composition is about whereas the solubility anddisintegration is 0.04 percent in accordance with the A.D.A.Specification No. 9 test for Dental Silicate Ce ment. colorless flintglass (refractive index 1.5795), the X-ray When part of the fused silicawas replaced with 3,194,784 Patented July 13, 1965 ice opacity wasbetween that of enamel and dentin without visual differences in color oropacity. When 5 parts benzoyl peroxide per 100 parts resin was used with74 to 83 percent vinyl silane treated silica, the compressive strengthaveraged 22,000 p.s.i.

METHODS OF PREPARATION Materials The filler.Clear, colorless, fusedsilica was selected as the reinforcing filler because of its lowcoefiicient of thermal expansion as well as other desirable propertiessuch as strength and inertness. It is less likely to be abrasive thanaluminumoxide or crystalline quartz since its hardness is only about 4.9on the Mohs scale.

The fused silica particles utilized in this invention can be produced bycrushing and reducing to powder, in any conventional manner, the clear,colorless, fused quartz (silica). All impurities or contamination withiron or other foreign materials should be avoided or removed after thepowder is formed. The fused silica particles should be fine enough topass through a number 325 sieve of the US. Standard Sieve Series.

The keying agent.When it is desired to optionally incorporate a keyingagent with the filler, the quartz particles produced by theaforementioned step are sifted and treated with a high performanceethylenically unsaturated organosilanol finishing or keying agentsuitable to the organic polymer. For example, an aqueous solution oftris (Z-methoxy ethoxy) vinyl silane may be catalyzed with sodiumhydroxide to give a pH of 9.3 to 9.8, one-half percent of the silane perweight of the fused 'quartz being used.. The slurry is dried at 125 C.and

cooled, 1.25 percent. by weight of benzoyl peroxide is then dispersedtherein. Vinyl trichlorosilane, with or without suitable elastomeric ormodifying agents, such a silica particles and the organic polymer.

As an example of a keying agent utilizing vinyl trichlorosilane, forexample, 3 percent vinyl trichlorosilane is used with 1 percent of thebinder, hereinafter to be discussed in detail, and 1 percent of apolyisocyanate compound. These materials are dissolved in methylmethacrylate monomer and mixed withsilica, the excess monomer is allowedto evaporate. The product is then heated to 100 C. forone hour afterwhich it is cooled,

As a specific example, two or more moles of glacial methacrylic oracrylic acid may be reacted with one mole of the diglycidyl ether of abisphenol, such as 4-4-dihydroxy-diphenyl-2,2-propane, or other similaror analo- "gous epoxide-containing compound.

Other suitableexamples of epoxide-containing compounds includessubstances having the formulas:

O CHz-O- 3,194,784 a 3 4' 3,4-epxy-6 methyl cyclohexylmethyl-3,4-epoXy-6 meth- EXAMPLE 2 V yl cyclohexane carboxylate, whereinS refers to saturated As another example of a msthod fur synthesizingthe mugs polymerizable intermediates used in connection with the presentinvention, the condensation of the sodium or H other salt of bisphenol A(bis[-4-hydroxyphenylIdimeth- I yl methane), or other suitable phenoliccompound, CH3 with an equivalent amount of the reaction product ofglycidyl methacrylate or glycidyl acrylate and anhydrous hydrochloricacid may be made in accordance with the dl-Limonene dioxide, 10following formula:

r H a r H eo H- H o& H 0 H Hi|J-H N NaO-C 0( 30 CONa 201' more(O1-([Ji|:( Jo|:-c=(IJ-H) Jul H0-H H H H 0 H HH H HH H H 7 HH H H1 1 rlrIII H-(|)H H 3) III (HJ H( I1-H CC Eli o H H-O-HvH(lJ=C(|JO(lE'J3-(l30-O C-CIJC C-O-G( |J,Cll.OO i =(|JH NaCl H H H HCC]? H(|3-H H H H H HH H i The sodiumchloride may then be removed fromthe reaction product by washing in any conventional manner. 0 o aEXAMPLE 3 30 A preferred method of synthesizing this polymerizable1:4-cyclohexadiene dioxide and intermediate, or monomer is given by thereaction HH H HH 7 H t t a O\ H H %0o\ /0\' H H H DMPT N3 HOC/ \C--(JCC-O-H 201' more (HC--CJJOCJJ=CH) l l l 1 60 0.

(HID HoH H H H 0 HH H HH H H HH H HH H 'H l l B 2 l l 5 J HCH Hotlt CH|H 0c H E HH HC=( JOI-OCJIJCOC 00o\ o-o0-00o(l;- :C-H

H o 1 1 H H H( |7H 00 H 1'1 1 1 d HH H HH /0\ /0\ wherein two moles ormore of -glycidy1 methacrylate are CHz--CH-GHqCH--CH combined with onemole of bisphenol A, or other suit- 1;4- i able, phenolic compound, and05 to 1.0 percent or more To this reaction is then added about 0.5 to1.0 percent of a tertiary'amine, such as dirnethyl-para-toluidene. ormore of a tertiary amine, such as dimethyl-para- Other suitablephenolic'compounds include substances toluidene, which catalyzes theabove methacrylic or h i the f r ul acrylic acid addition to theindicated epoxide groups 1 i and also activates the peroxide catalystwhen, at a later time, hardening or solidifying of the materialisdesired. These ingredients (the methacrylic acid, epoxide and i 3 amine)are stirred and held at approximately C. in I HO O OH the presence of afree radical polymerization inhibitor until a standard test for epoxideor acid indicates the 60 L 7 a 2 reaction 1s complete. The reactiontakes placeinv'acr cordance with the formula OOH Y H i H a t i /OC\H(l}' H/OC\ I II-(FE DMPT H-C.-C|J-(|1OO 0(I1V-O O--O(|1(3(|J-H 2 or more(HO.OOC=(IJ-H) v H H H oH H H H H 7 HH H HH i t i i H a a H H(|3H 1'1Eli cO H-( JH 0C 1 1 o 1 1 H-+%H H-o=c([?0 t C|--(|JC|-,OG C(l30CO(|3'VC (|3-0-O-C=C-H H 0 HHH H JH H-r r E ii H HH H HH Diphenolic acidor HOQOH OH Phloroglucinol.

- C. with continual stirring until the reaction is complete inaccordance with the following new test.

In said test a few drops of the reaction product are mixed with enoughfused silica powder (or other reinforcing filler), which containsapproximately 2 percent benzoyl peroxide, to produce a stiff paste. Thiscomposition is then placed between two films of polyethylene, or is insome other way protected from atmospheric oxygen, and thereafter heatedto 90 C. A negative test is indicated by the sample failing to hardenwhereas in a positive test the sample hardens within minutes. Thephenolic hydroxyl groups inhibit free radical polymerization until thephenol groups are used up (etherified) by the addition reaction with theoxirane (epoxy) groups.

When a positive test indicates the reaction, as described in any of theaforementioned examples, is complete, approximately 0.006 percenthydroquinone is added to prevent premature polymerization of themethacrylate or acrylate groups. The hydroquinone is dissolved in enoughconcentrated hydrochloric acid to react with any excess or remainingepoxide groups.

The reaction product is then reduced in viscosity to a medium syrup bythe addition of methyl methacrylate, ethylene or tetraethylene glycoldimethacrylate or other suitable reactive diluents.

The syrup or resin intermediate is then ready for use with the treatedfused silica powder containing benzoyl peroxide or other suitablecatalyst.

A period of 3 to 10 minutes expires between the start of the mix and thetime the material hardens. However, this time may be reduced by addingmore activator (dimethyl-para-toluidene or para-toluene sulfinic acid).On the other hand, hardening time may be lengthened by washing out someof the dimethyl-para-toluidene or other tertiary amine catalyst with adilute aqeous hydrochloric acid solution.

To use the material, the treated silica powder, containing a suitablecatalyst, such as about 1.25 percent by weight benzoyl peroxide, ismixed with the sirupy liquid organic material (heretofore described)which contains a suitable activator, such as dimethyl-para-toluidene orpara-toluene sulfinic acid, and the mixed aggregate is promptly placedin the cavity to be filled, wherein it hardens at mouth temperaturewithin 10 minutes by polymerization of the organic material.

Properties of the materials Setting time.-The setting time is defined asthe number of minutes elapsed from the starting of the mix to the timewhen the point of a penetrating instrument, such as the point of aGilmore needle, fails to make a perceptible indentation on the surfaceof the specimen. Setting times were determined either at roomtemperature or at 37 C. When 70-80 percent of the powder was mixed withthe liquid resin it hardened within ten minutes at 37 C.

Compressive strength.The compressive strength was tested according tothe American Dental Association Specification No. 9 for Dental SilicateCement. The compressive strength was found to be higher using the cinylsilane treated powder than when untreated powder was used, especially ifthe specimens were stored in water for 7 days.

With the vinyl silane treated silica, the particle size influenced thecompressive strength. Specimens made with coarse particles (thosepassing U.S. Standard Sieve No. but retained on No. 325) gave 15,000pounds per square inch, while specimens made with fine particles (thosepassing U.S. Standard Sieve No. 325) gave 23,000 p.s.i. Specimensprepared from a mixture of the particles showed an intermediate strengthof' 19,000 p.s.i.

Solubility and a'is'integratioh.Solubility and disintegration weretested in accordance with the aforementioned A.D.A. Specification No. 9for Dental Silicate Cement except that the weighing bottles were weighedafter drying at 99 C. and C. to detect organic leach products that mightbe driven ofi at the usual 149 C. The solubility was 0.00 to 0.08percent by weight.

Coefiicient of thermal expansion-The coefiicient of thermal expansionwas measured on three specimens containing 70 percent vinyl silanetreated fused quartz. The average was 24 10 (p.p.m.) per degree C.between 30 C. and 40 C.

Hardening shrinkagel-Polymerization or hardening shrinkage tests weremade using the dilatometer method developed by Smith and Schoonover. Thevolumetric shrinkage was about 2 percent (measurements were taken onfour specimens wherein the time varied from the first measurement, atabout 3 minutes to 60 minutes from start of mix) at 37 C. when the mixcontained 66 percent vinyl silane treated fused silica by weight. Thisvalue of 2 percent is tentative until further tests over longer timeintervals are made.

Color stability.Color stability was tested by 24-hour exposure of halfof each set of specimens to the ultraviolet source described in AmericanDental Association Specification No. 12 for Denture Base Resin, and bycomparison with the other half of the specimens that had been shieldedwith aluminum foil tape.

The color change was less than that produced in comparable mixes madewith a self-curing methyl methacrylate syrup mixed with the treatedsilica. In both cases the color change was believed to be due to thedimethyl p-toluidene activator.

The use of one percent of a commercial ultraviolet absorber per weightof the synthetic resin prevented color change produced by theultraviolet lamp without affecting the hardening time.

Opacity.The visual opacity when tested according to the ADA.Specification No. 9 for Dental Silicate Cement was slightly above 35percent (C The X-ray opacity could be raised to approximate toothstructure by using 20-30 percent of clear, colorless, flint glasscontaining about 35.5 percent of lead oxide. This would not perceptiblyaffect the color or visual opacity.

Any reinforcing filler, pigment or other inclusion, in a resin-bondedmaterial, should be treated with a suitable keying agent or finish thatis capable of forming stable chemical bonds to both the resin and theincluded material. In the case of vinyl silane, the hydrolized siliconecan combine by condensation with the surface of the fused silicaparticles, exposing vinyl groups which can copolymerize with the resinwhen it hardens. Illustrating this, the silica-resin material wasallowed to harden on the surfaces of glass slides that were vinyl silanetreated and controls that were untreated. They were then immersed inwater. The patches of material came loose from the untreated slideswithin two days but adhered to the treated glass surfaces for a year.

Glass surfaces and fused silica powder that have been treated with vinylsilane are water repellent; when untreated, it clean, they are veryhydrophilic.

If the surfaces of pigment or filler particles have, by their nature,greater afiinity for water than they have for the organic resin binder,they will be sources of stress concentration and mechanical weaknesswhen serving in the moist oral environment. 7 V

It should be understood, of course, that the foregoing disclosurerelates to only preferred embodiments of the invention and that it isintended to cover all changes and modifications of the examples of theinvention herein chosen for the purposes of the disclosure, which do notconstitute departures from the spirit and scope of the invention.

What is claimed is:

1. A dental filling material comprising about 17% to about 30% by weightof a hardenable resin and about class consisting of tris(2-methoxyethoxy) vinyl shame and vinyl trichlorosilane.

3. A dental filling material comprising about 17% to about 30% by weightof a hardenable resin and about 83% to about 70% by weight of a filler;saidresin com:

prising the reaction product of at least one member of the classconsisting off3,4-epoxy-6 methyl cyclohexyl methyl-3,4-epoxy-6 methylcyclohexane carboxylate, d1- Limonene dioxide, 1:4 cyclohexadienedioxide, and 1:4- pentadiene dioxide, at least one member of the classconsisting of methacrylic and acrylic acids, a tertiary amine catalyst,and a free radical polymerization"inhibitor consisting essentially ofhydroquinone; said filler comprising a mixture of fused silica and aperoxide catalyst,

I 4. A dental filling, material as set rforthrin claim 3,.

wherein said fused silica is treated with. a member of the classconsisting vof tris(2-methoxy ethoxy) vinyl silane and vinyltrichlorosilaner I References Cited by the Examiner UNITED STATESPATENTS 2,824,851 2/58 Hall j 260-455v 3,066,112 11/62 Bowen 260-41FOREIGN PATENTS 710,535 ,6/54 Great Britain.-

MORRIS LIEBMAN, Primary i Examiner.

ALEXANDER H. BRODMERKEL, Examiner.

1. A DENTAL FILLING MATERIAL COMPRISING ABOUT 17% TO ABOUT 30% BY WEIGHTOF A HARDENABLE RESIN AND ABOUT 83% TO ABOUT 70% BY WEIGHT OF A FILLER;SAID RESIN COMPRISING THE REACTION PRODUCT OF A POLYGLYCIDYL ETHER OF APOLYHYDRIC PHENOL, AT LEAST ONE MEMBER OF THE CLASS CON SISTING OFMETHACRYLIC AND ACRYLIC ACIDS, A TERTIARY AMINE CATALYST, AND A FREERADICAL POLYMERIZATION INHIBITOR CONSISTING ESSENTIALLY OF HYDROQUINONE;SAID FILLER COMPRISING A MIXTURE OF FUSED SILICA AND A PEROXIDECATALYST.